package day25;

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLong()) { // 注意 while 处理多个 case
            long n = in.nextLong();
            long sum = 10;
            while(sum >= 10) {
                sum = 0;
                while(n > 0) {
                    sum = n % 10 + sum;
                    n = n / 10;
                }
                n = sum;
            }
            System.out.println(sum);
        }
    }
}